Water and the Aztec Landscape in the Valley of Mexico

This article has generously been specially written for us by Barbara Mundy, Associate Professor of Art History, Fordham University, New York. The story of water management (or the lack of it) in the central Valley of Mexico is both intriguing and tragic...

Pic 1: Map of the Valley of Mexico, circa 1492 (Click on image to enlarge)

The Valley of Mexico has been home to two of the world’s largest cities. In the fifteenth and early sixteenth centuries, the Aztecs ruled much of Mexico from their island capital of Tenochtitlan; today, spreading over the ruins of that same city is Mexico City, a city of some 25 million people. The rise of Tenochtitlan in the fourteenth century depended upon an ecological miracle, the manipulation of a salty inland sea to create large zones of freshwater lakes and irrigated fields, whose crops sustained the peoples who lived in the many cities and towns of the Valley. The large inland sea that once dominated the Valley stretched some 60 kilometers from north to south - a connected system of five shallow bodies of water that were called lakes, but differed from true lakes in that they had no natural outlets to the sea (pic 1). These lakes swelled during the rainy season (June through October) with water coming in from rivers, streams and rainwater; evaporation into the air and absorption into the ground allowed the waters to recede. On the map, they appear as an enormous unified system, but there were significant differences between them.

Pic 2: Close-up section of a ‘chinampa’, Xochimilco, nr. Mexico City (Click on image to enlarge)

The two connected lakes to the south, Lake Chalco and Lake Xochimilco, were freshwater lakes. Probably starting about 800 years ago, the people living along their edges began to create raised beds for growing maize, squashes, and vegetables. These beds were called chinampas and they were made by scooping up the mucky soil from the swampy areas on the edge of the lake and piling it up into rectangular mounds. Around the edge of these mounds, the farmers planted trees to hold the raised soil. When the water levels rose, as they did every year during the rainy season, the areas where they had removed the chinampa soil became irrigation canals. The nutrients that had collected on the bottom of the lake from silt and rotted plants meant that these beds were extremely fertile.

Pic 3: Artist’s impression of the landscape surrounding Tenochtitlan: the dike of Mexicaltzinco can be seen bottom left (Click on image to enlarge)

But their fertility was a fragile state: the three lakes that lay to the north, Tetzcoco, Xaltocan and Zumpango, were salty, and if saltwater washed into the southern lakes during floods, it would kill plants and ruin soil. Thus, the peoples of the southern lakes joined together to create a short (about three kilometer) dike and causeway (or raised road that functioned as a dike) across a natural bottleneck in the lake system. This so-called dike of Mexicaltzinco ran from the flanks of Huixachtitlan (Hill of the Star) near Culhuacan to Huitzilopochco (now called Churubusco), thereby sealing off and protecting their sweet water system.

Pic 4: 16th century map of part of the Chalco region; Archivo General de la Nación, Tierras vol. 2681, exp. 6 (Click on image to enlarge)

Over time, the chinampas stretched out from over the shores of the lakes of Chalco and Xochimilco; the map of a part of the Chalco region, taken out of a law suit (pic 4) and now housed in the Archivo General de la Nación in Mexico City shows how organized they were in the sixteenth century. A large blue canal, filled with freshwater, rings the perimeter of the fields; the artist has shown the large trees that served as boundary markers and to hold the soil. The grey stripes, running both vertically and horizontally to slow the flow of water, are the chinampas. Among them are small “islands” ringed in green. These are the high grounds, and the small houses, drawn native style, on the three lower ones, and church on the top, stand for the small settlements that were interspersed among the irrigated fields. The red lines and measurements (hands and dots) are used to single out an area under contest in the lawsuit.

Pic 5: Model of chinampa agriculture, National Museum of Anthropology, Mexico City (Click on image to enlarge)

By the time the Spaniard conquistadors arrived in 1519, the edges of Chalco and Xochimilco were filled by kilometer upon kilometer of these “floating gardens,” and Spanish soldiers like Bernal Diáz del Castillo would later write about these “large maize plantations lying near the lake.” Some chinampas still exist today, to the south of Mexico City.

Because of chinampa agriculture, the southern lakes became the breadbasket of the larger Valley, supplying their northern neighbors around the lakes of Tetzcoco, Zumpango and Xaltocan with fresh vegetables, squashes, chiles, and corn throughout the year.

Pic 6: In an early rebellion under Aztec rule, Chalco destroyed four Mexica canoes with rocks and killed five Mexica men: Codex Mendoza, folio 4v (detail) (Click on image to enlarge)

The value of chinampas was not lost on these neighbors, particularly the people living on the island of Tenochtitlan, in the center of the lake. These peoples called themselves the Mexica and history knows them as the leaders of the Aztec empire, which was ruled from their island city. One of the first moves of the ruler Moteuczoma I (r. 1440/1-1469), as he consolidated the power of the warmongering Mexica in the Valley, was to provoke the city of Chalco so he could declare war against them. By defeating Chalco in the 1440s, Moteuczoma thereby secured the great agricultural resources of the southern lakes for the benefit of the peoples in his growing city.

Pic 7: Part of the remaining chinampa network at Xochimilco today (Click on image to enlarge)

Seeing the Chalco miracle, Moteuczoma attempted to create freshwater zones around his island city, so they could also have chinampas. This would seem, on the surface, impossible, since Tenochtitlan sat within the salty lake of Tetzcoco. But residents undoubtedly noted a natural phenomenon that occurred in the lakes. Because freshwater streams and springs flowed into the lake of Tetzcoco from the western side of the Valley, the water in the western part of the lake was relatively sweet, growing progressively more salty toward the east. But during the rainy season, salty water rushing into the lake of Tetzcoco from Lake Zumpango and Xaltocan would turn the whole system salty again.

Pic 8: Artist’s impression of building a causeway near Tenochtitlan; illustration by Alberto Beltrán (Click on image to enlarge)

By building a system of dikes and causeways, barriers of raised earth, the latter serving as roads that ran roughly north-south, city builders were able to protect the waters around Tenochtitlan from this salty backflow. Gradually the yearly flows of freshwater from the west diluted the saltwater out of the system, making this water suitable for growing plants in gardens and plots in and around the city of Tenochtitlan (although it seems to have been too salty or brackish to drink). There were two sets of dikes that created this protected “Laguna of Mexico.”

Pic 9: Monument believed to commemorate the dike of Ahuítzotl, National Museum of Anthropology, Mexico City (Click on image to enlarge)

The first was the longest, running some seventeen kilometers north-south though the Lake of Tetzcoco. It was probably built in the mid-fifteenth century and called the dike of Nezahualcoyotl for the Tetzcocan king who engineered it. The second dike offered added protection. It ran within the area protected by the dike of Nezahualcoyotl to link the causeway of Tlalpan to the south to the causeway of Tepeyacac to the north with a stone wall that ran along the eastern edge of Tenochtitlan. It was called the dike of Ahuitzotl for the Aztec emperor who commissioned it around 1498-99.

The happy result of these waterworks can be seen in a map of Tenochtitlan painted perhaps in the 1540s. In the detail shown in Picture 10 one can see the eastern edge of Tenochtitlan running horizontally (the map is oriented with west at top). The stone wall of the dike of Ahuitzotl runs along the border of the city, whereas the wall of the dike of Nezahualcoyotl runs in the middle of the lake. The artist has been careful to clue the differences in water quality using pigment. This zone between the dikes is sweet, and shown by the application of a rich blue pigment, likely an indigo-based color called Maya blue, because of its origins in the Maya region to the south. The zone at the bottom of the image, the salty water of the Lake of Tetzcoco, is shown with the application of a muddier, greenish color. The artist also shows the richness that the lakes provided, as figures in boats trap birds and fish with exuberance.

The creation of these waterworks was a feat of ancient engineering akin to the construction of the great pyramids of Egypt. They relied on subtle differences in environmental conditions - like the flow of freshwater into the system, and the slightly higher elevations of the southern lakes and the western shores, which meant that water flowed from south to north and west to east. The peoples of the Valley were used to living with the water and used it to their advantage. In order not to impede the west-to-east flow of water in the Laguna of Mexico, the Mexica ran canals that ran west to east through their city; these proved useful for transport through the growing metropolis. Such a system of dikes and canals required constant maintenance and upgrading. Work on cleaning and maintaining the system was part of the labor obligation - a kind of tax paid by working--of many towns in the Valley.

Another part of this system was the great causeways that ran across the lakes and connected the numerous cities and islands within the Valley. These served as dikes to control the flow of water in the system. Two of the most important of these causeways were those of Tlacopan (now called Tacuba) and Nonohualco, both of which ran from the eastern shore to the island of Tenochtitlan. In a parallel set of inset canals that ran along them like the painted lines on a road, these causeways carried vital streams of fresh drinking water. The causeway of Tlacopan carried water from the springs at Chapultepec to Tenochtitlan; the northern causeway carried water from a spring called Xancopinca, near Azcatpotzalco to Tlatelolco, to the north of Tenochtitlan.

Pic 13: Artist’s impression of water-carrying by canoe; archaeological remains of a Mexica canoe (below) and of a model canoe (top right), National Museum of Anthropology, Mexico City (Click on image to enlarge)

These raised causeways had breaks allowing the lake water to flow under them, spanned by bridges. At these breaks, the precious freshwater was carried across via great hollowed-out logs that spanned from one side of the canal to the other. At certain points where the water crossed a gap on these log bridges, the water sellers could gather in their canoes on the canal beneath and fill their large ceramic water jugs, and then take the canal route to the city’s markets or for home delivery.Because travel by water is faster and more efficient than travel by road, canoes moved most of the goods through the Valley. Some of these were quite large, and Bernal Diáz wrote of canoes that were “hollow troughs cleverly cut out from huge single logs, and many of them would hold forty Indians.”

Pic 14: Artist’s impression of part of the canal network linking chinampas around Tenochtitlan (Click on image to enlarge)

During the dry season, when water levels dropped throughout the Valley, and the lakes resembled shallow swamps rather than lakes, boatsmen relied on canals dredged out of the lakebed so that they could move produce and goods between cities in the Valley. Canoe travel happened almost entirely at night to avoid the hot tropical sun; for instance, boatsmen would load their canoes in Chalco at dusk, and travel through the night to arrive at Tenochtitlan’s markets by dawn.

Pic 15: The battle of Nonoalco, Florentine Codex, Book XII (Click on image to enlarge)

The great lakes of Mexico were turned into a battleground during the Spanish conquest of the Valley in 1519-1521. Spaniards, and their indigenous allies, built great warships to attack Tenochtitlan by water, and they smashed the aqueducts of Chapultepec and Nonohualco, depriving the city’s residents (there were perhaps 150,000) of the life giving water during the agonizing siege of the spring and summer of 1521. Victory declared, the conquistadores, many of whom were from bone-dry regions of Extremadura in Spain, paid little attention to the careful co-existence with water that peoples of the Valley had cultivated for generations.

Pic 16: The Spanish-built fountain (known today as the ‘Salto de Agua’) at the end of of a native aqueduct, bordering the historic city centre, pictured late 19th century (Click on image to enlarge)

Instead, they started a new war against the water in the Valley. This war lasted over 400 years, as Spaniards and their Creole descendants tried to get rid of all of the water by draining the lakes. They searched fruitlessly for drains (thinking the lakes were like bathtubs with a plug), built tunnels through the mountains that caved in, changed the courses of rivers, all in an attempt to dry up the Valley, perhaps to turn it into bone-dry Extremadura of their ancestors.

Pic 17: Smog hovering over Mexico City today (Click on image to enlarge)

The great project of the “desagüe” was successful in that by the early 20th century most of the lakes were gone, subterranean pumps working night and day to pipe water out of the Valley via tubes that cut through mountains. Today, Mexico City suffers from both chronic flooding and a shortage of freshwater; the problems once solved by the great engineers of the ancient Aztecs are at hand again.

The lake was never mapped using the precise survey tools available today, so the contour of the lake that we see on today’s maps is a reconstruction, based on the position of towns that we know were once at the shore of the lake, and geographic contours. One of the best reconstructions was created by Luis González Aparicio, in his Plano reconstructivo de la región de Tenochtitlan (Mexico City: Instituto Nacional de Antropología e Historia, 1973). González Aparicio’s work has been advanced by Tomás Filsinger, whose maps have been featured in Mexicolore.This said, the lake was a shallow one, and much of its edge was defined by broad swaths of wetlands that filled and emptied according to the season. Cartographers like hard, defined boundaries, and the Lake of Texcoco didn’t have one. Moreover, the lake was emptied over time, so the lake of the Aztec city was much diminished by the 18th century, and so looks different in maps of that era.

4 At 12.24am on Wednesday August 3 2016, Zigmond wrote:

What was the actual shape of Lake Texcoco at the time the Aztecs came to dominate the Valley of Mexico?I’ve seen a lot of maps of the lake and its surrounding on the web but the outline varies significantly between the maps. The map in this article has the year 1492. How can you be certain it is the correct shape of the lake?

3 At 10.21am on Thursday May 21 2015, Keegan wrote:

Thanks for the quick, helpful response! By the way, this particular article is perhaps my favourite on this website--Gotta love geography! Also, what’s wonderful about this site is that so many of the scholarly authors in my Aztec library make the effort to answer questions here. Cheers!

2 At 1.16pm on Wednesday May 20 2015, Keegan Dowling wrote:

How did the design of the Dike of Nezahualcoyotl differ from the design of causeways within the Laguna de Mexico? Were there bridges/gaps/gates in it? What was the procedure for canoes to traverse the Dike? (And where would I find this info in the primary sources)? Thanks!

Mexicolore replies: The dyke, some 8 metres across and 4 metres high, closed off the whole of the western Lake Texcoco. If you study the Map of Tenochtitlan (pic 10 above) or the (1550) ‘Mapa de México’ - also known as the Uppsala Map - you can see the dyke still successfully functioning up to a century after it was built. There appear to be no gaps in it (its purpose was purely to separate the freshwater from the salty water so would presumably not have had bridges or crossing points). A good book to consult on this would be Desarrollo Urbano de México-Tenochtitlan Según las Fuentes Históricas by Sonia Lombardo de Ruiz, SEP-INAH, Mexico, 1973.